Several fish species such as the medaka, fugu and zebrafish have become popular as models organisms for developmental studies. Some of the reasons for their popularity are, they are vertebrates (hence more significant to human research than invertebrate models such as fruit flies), and they have short developmental periods. And since these fishes lay eggs, they allow studies on development of the embryos (inside the eggs) outside of the mother's body. Of these models, the zebrafish is increasingly becoming the model of choice for many researchers. The egg laying in these fishes, can be manipulated using artificial light and periods as females lay their transparent eggs within about an hour after the light comes on (i.e., ‘dawn’) after a dark cycle. An electronic timer usually controls the light cycles in 14 h light and 10 h dark cycles in the environment in which the fish are housed. Noting the popularity of fish models, several manufacturers have developed aquatic housing where these models can be raised.
Rack type fish housing has been available from many manufacturers in which clear tanks are used to rear fishes. The advantage in such a system is that a plurality of clear tanks can be placed on the racks. That the tanks are clear allows a common light source to be used for all the tanks. But a significant disadvantage is that all tanks are subject to the same light cycle as the room or chamber (or within curtains) in which they are housed with the common lighting source. Thus if the ‘dawn’ is set to come at 10 A.M., then eggs are laid from about 10-11:30 A.M. in all the tanks in that rack. An egg laid and fertilized at about 10 A.M. will have 3 hours of growth post fertilization at about 1 P.M. on the same day. If a researcher or user wishes to observe egg development at say 12 hours post fertilization in a rack unit whose ‘dawn’ is at 10 A.M., then the researcher will need to come at 10 P.M. of the same day, thus posing a severe inconvenience. Similarly, some researchers may come in at an earlier time to 10 A.M., but will have to wait till 10 A.M. or later to collect eggs from any tank.
In addition, none of the systems conveniently integrate fish housing with harvesting eggs or embryos. Eggs are often the only purpose for which the fish are maintained and hence lack of an integral ability to conveniently collect them or automate the process of collecting them constitutes a substantial drawback in the art. For instance, in some of the prior art, a bed of marbles is laid in the tanks where the fish are housed by a researcher (user), which prevents the eggs that are laid from being eaten by adult fish. In this arrangement, the eggs are harvested by the researcher using a gravity driven siphon. The siphoned eggs are collected in a net and transferred to a suitable tank or container. Alternatively, a small dish or similar container with a net stretched across its open face maybe placed by the researcher/user within the tanks. The net has mesh of a size (say 2-5 mm) that prevents the adult fishes from scavenging the eggs, while allowing the laid eggs to drop below the net and into the container. In this case, after the eggs are laid (within about an hour after ‘dawn’), the user physically removes the dish containing the eggs from the tanks.
Both these arrangements require frequent physical intrusions by the researcher on the fish habitat for purpose of harvesting eggs, an inconvenience for the researcher as well as stressing the fish, thereby affecting their well being. Also, toxins or foreign substances could be unwittingly introduced by the researcher into the water whenever eggs are harvested by this method. In the same token, any infection or toxin in the water could potentially affect the researcher.
Moreover, researching these eggs includes many drawbacks. The embryos of the fish are transparent and can be observed under a microscope if placed on a small drop of water or suitable solution. There is no slide that allows easy visualization of these embryos.
Therefore, needs remain in this area of technology.